The present invention relates to a safety programmable logic controller (PLC) having an I/O module to which a safety device for detecting a predetermined condition at any time is connected or a CPU module for executing a safety program (e.g., a sequence program), and more particularly, to an authentication control for authenticating the safety program when the safety program is automatically created.
Recently, a safety function is commonly introduced into a system controller using a programmable logic controller (PLC). The safety function includes, for example, a function for duplexing a CPU, an MPU, or various processing units to allow the processing result to be appropriately output, and a function of safely stopping a system by halting a system operation or a feed operation when an emergency condition occurs in the system, and the like. For example, the emergency condition may occur when an emergency stop switch is pressed or when a sensor such as a light curtain detects invasion of a person.
For example, a safety PLC introduced for organizing such a system is disclosed in a patent document 1, in which a hardware construction is duplexed. Hereinafter, a sequence program for controlling the safety PLC is referred to as a safety program. A standard for creating a safety program has been published from, for example, an international electrotechnical commission (IEC). Conventionally, in order to produce a safety program which satisfies this standard, a high level of technical knowledge for the safety standard or experience of producing the safety program is required.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-358106
As a new technology for obtaining a high quality safety program having a high level of safety and reducing burdens of programmers for obtaining the aforementioned safety program, a method for automatically creating a safety program can be conceived. Nevertheless, even when the safety program can be automatically created on the safety PLC, an administrator (having a license) of the safety program that has been automatically created should perform a safety authentication procedure.